Prolonged computer use, especially if fatigue ensues, is associated with visual and musculoskeletal symptoms. The aim was to determine the time-course of perceived fatigue in the wrist, forearm, shoulder and eyes during a 60-min mouse task (painting rectangles), and whether object size and/or mouse use demands were of influence. Also, we investigated performance (number of rectangles painted), and whether perceived fatigue was paralleled by local muscle fatigue or tissue oxygenation. Ten women performed the task for three conditions (crossover design). At condition 1, rectangles were 45 × 25 mm, square paint cursor size 1.3 × 1.3 mm, and mousepointer movement ratio 1:26. At condition 2, the same cursor size and mousepointer movement ratio was used, but rectangles were smaller. At condition 3, the smaller rectangles were used, but the cursor size was also smaller and mousepointer movement ratio was 1:8. The results showed increased self-reported fatigue over time, with the observed increase greater for the eyes, but no change in physiological responses. Condition 2 resulted in higher performance and increased eye fatigue. Perceived fatigue in the muscles or physiological responses did not differ between conditions. In conclusion, computer work tasks imposing high visual and motor demands, and with high performance, seemed to have an influence on eye fatigue.

Previous studies have shown an association of visual demands during near work and increased activity of the trapezius muscle. Those studies were conducted under stationary postural conditions with fixed gaze and artificial visual load. The present study investigated the relationship between ciliary muscle contraction force and trapezius muscle activity across individuals during performance of a natural dynamic motor task under free gaze conditions. Participants (N = 11) tracked a moving visual target with a digital pen on a computer screen. Tracking performance, eye refraction and trapezius muscle activity were continuously measured. Ciliary muscle contraction force was computed from eye accommodative response. There was a significant Pearson correlation between ciliary muscle contraction force and trapezius muscle activity on the tracking side (0.78, p < 0.01) and passive side (0.64, p < 0.05). The study supports the hypothesis that high visual demands, leading to an increased ciliary muscle contraction during continuous eye–hand coordination, may increase trapezius muscle tension and thus contribute to the development of musculoskeletal complaints in the neck–shoulder area. Further experimental studies are required to clarify whether the relationship is valid within each individual or may represent a general personal trait, when individuals with higher eye accommodative response tend to have higher trapezius muscle activity.

The present study aimed to identify whether or not an increase in ciliary-muscle contraction force, when the eye-lens is adjusted for viewing at a near distance, result in an increase in trapezius muscle activity, while performing a natural work task. Twelve participants, ranging in age from 21 to 32 years, performed a computer-mouse work task during free gaze conditions. A moving visual target was tracked with a computer mouse on a screen placed at two different distances from the eyes, 25 cm and 50 cm. Tracking performance, eye accommodation, and bilateral trapezius muscle activity were measured continuously. Ciliary-muscle contraction force was computed according to a formula which takes into account the age-dependent, non-linear relationship between contraction force of the ciliary muscle and the produced level of eye accommodation. Generalized Estimating Equations analyses were performed. On the dominant hand side and for the nearest screen distance, there was a significant effect of ciliary-muscle contraction force on the trapezius muscle activity (p<0.001). No other effects were significant (p>0.05). The results support the hypothesis that high visual demands, during computer mouse work, increase ciliary muscle contraction force and contribute to a raise of the sustained level of trapezius muscle activity. The current study specifically clarifies the validity of the relationship between ciliary-muscle contraction force and trapezius muscle activity and demonstrates that this relationship is not due to a general personal trait. We conclude that a high level of ciliary muscle contraction force can contribute to a development of musculoskeletal complaints in the neck-shoulder area.

We intended to assess consequences of reduced visual acuity for performance in a natural simple motor task (tracing) using objective kinematic performance measures. Specifically, we intended to elucidate the kind of relationship between the task performance and best corrected binocular visual acuity and to determine the threshold of visual acuity when task performance starts to deteriorate.

Methods

Ninety-five individuals with different best corrected visual acuity participated in the study (age 49 ± 12 years, mean ± SD, 27 men and 68 women). The participants manually traced maze-like visual patterns of different spatial complexity presented on the screen of a portable notebook computer using Clinical Kinematic Assessment Tool software. Tracing error was computed as performance measure in each trial with a spatial pattern matching technique – rigid point set registration method.

Results

The segmented linear regression analysis showed that the relation between visual acuity and tracing errors was best described with a regression function having a break point between two data segments. Tracing performance was unaffected by values of visual acuity below 0.2 on logMAR scale, but when logMAR values increased above this critical limit (i.e. when visual acuity is further reduced), tracing errors linearly increased. The rate of the increase of the tracing error correlated with the complexity of visual stimulus shape.

Conclusion

Testing of fine motor functions with objective kinematic measures during visuomotor tasks may help differentiating between actual effects of reduced visual acuity on eye–hand coordination in individuals with similar levels of impairment of visual acuity.

The authors present a study of the relationship between individual variation in working memory capacity (WMC) and visually guided hand control in the face of visual distraction. WMC was assessed with the automated operation span task. Hand control was measured by requesting participants to track a visual target with a hand-held touch screen pen. Tracking error increased when nontarget visual objects (distractors) appeared, especially in individuals with low WMC. High-WMC individuals are less impaired by distractors than their low-WMC counterpart, because they resume target tracking more quickly after distractor onset. The results suggest that visual distractors cause a momentary interruption to tracking movements and that high WMC attenuates this interruption by facilitating visual search.

Fatigue is a phenomenon of pronounced importance in sports. Recently, there is strong evidence of interplay between the prefrontal cortex and motor output during fatiguing contractions. The dorsolateral prefrontal cortex (DLPC) due to its large involvement in cognitive and motor activities is believed to be involved but this requires physiological clarification. AIM: We investigated the relationship between DLPC activity - responses in oxyhemoglobin (HbO2) and total hemoglobin (HbT) measured by near-infrared spectroscopy (NIRS), and the vastus lateralis muscle (VL) activity - quantified as root-mean-square (RMS) of the EMG signal, during a fatigue protocol.

METHODS: Four male runners (32±12 yrs) with probes for NIRS over the DLPC and EMG over the VL performed a track running test at a constant speed to fatigue (exhaustion). The running speed was individually determined as the average speed of a 1200-m time trial performed ~3 days prior to testing. For NIRS changes in μmole/L of HbO2 and HbT were computed. The VL EMG-RMS of the contraction of each step was normalized as a percent of a submaximal reference contraction (%RMS), thus removing the non-activity between steps. Data of 10s epochs at 20, 40, 60, 80 and 100% of time for each lap were averaged for analyses. Regression analyses performed with HbO2 and with HbT as dependent variables and %RMS as the independent variable.

RESULTS: Over time there was an increase in HbO2 and HbT in the DLPC, and in VL-%RMS. Both HbO2 and HbT correlated strongly with EMG-RMS during running to fatigue (see figures below); p<0.001 for both.

CONCLUSION: The strong relationship between DLPC and VL activities during running to fatigue suggests the involvement of the DLPC in the central processing of fatigue.

Visual strain and discomfort may contribute to the generation of work-related musculoskeletal disorders among e.g. computer workers. A positive correlation on a group level between eye-lens accommodation and trapezius muscle activity has been reported. In this study we investigated the possibility of a direct, fast, connection between lens accommodation and trapezius muscles activity. The subjects focused alternately on Near and Far targets, with a mean switch time of 5 s, through four different lenses. The cross-correlation, R(tau) was computed, between the time signals of accommodation and electromyography (EMG) from 23 subjects. In the overall mean R(tau) of 736 curves, a small but significant correlation peak (0.019) with a delay (of the EMG signal) of about 0.3 s, revealed a small common component in the two signals. Among the lenses, the positive lens (3.5 D), showed the highest correlation peak (0.040). The correlation may be caused by a direct “hard-wired” connection between the ciliary and trapezius muscles. But it could also be caused indirectly by the subject’s need for a more stable head in a more demanding visual task. The latter is supported by the result that the correlation was the highest in the positive lens condition. The present correlation is however weak and it has probably a low practical importance.

Frequent use of digital information technology has an impact on eye- and neck/shoulder-discomfort. Studies with cross sectional and intervention design indicate an association between the two symptom categories. Still, whether visually demanding near work, per se, contributes to increased neck/shoulder discomfort remains a question of debate. The aim of this laboratory study was to assess if visually demanding experimental near work affects eye- and neck/shoulder-discomfort when the posture was adjusted for comfort and no movements were allowed. Thirty-three healthy subjects performed a visually demanding computer screen task (viewing task) under four different optical lens conditions: binocular -3.5 D and monocular -3.5 D, +3.5 D and ±0 D. During the experiment subjects were seated in an office chair (with neck support) that was individually adjusted for comfort. At baseline and after each viewing task, subjects reported their perceived eye- and neck/shoulderdiscomfort on Borg’s CR-10 scale. Results show a significant increase of eye discomfort between baseline and the first viewing task, and a significant increase in neck/shoulder discomfort from baseline throughout the first three viewing tasks. Further analysis is required to determent whether the neck/shoulder discomfort was induced by the demanding near work or the static posture, or a combination.

The relationship between activity in ocular muscles and activity in neck and scapular muscles that stabilizes gaze is well known. However, it is uncertain if ocular load per se contributes to increased muscle activity in the neck and scapular area. Sixty-six participants performed a fixation task under three different conditions: binocular with minus lenses (-3.5D) and monocular with minus lens (-3.5D) and neutral lens (±0D). Ocular accommodation and trapezius muscle EMG were measured. Multiple regression analysis showed that response diopters accounted for 11.6% (p=0.009) of the variance in EMG in the binocular condition. In the monocular conditions, there were no significant relationships.

PURPOSE: To evaluate the reliability and validity of the 15-item Visual, Musculoskeletal, and Balance Complaints Questionnaire (VMB) for people with visual impairments, using confirmatory factor analysis (CFA) and with Rasch analysis for use as an outcome measure. METHODS: Two studies evaluated the VMB. In Study 1, VMB data were collected from 1249 out of 3063 individuals between 18 and 104 years old who were registered at a low vision center. CFA evaluated VMB factor structure and Rasch analysis evaluated VMB scale properties. In Study 2, a subsample of 52 individuals between 27 and 67 years old with visual impairments underwent further measurements. Visual clinical assessments, neck/scapular pain, and balance assessments were collected to evaluate the convergent validity of the VMB (i.e. the domain relationship with other, theoretically predicted measures). RESULTS: CFA supported the a priori three-factor structure of the VMB. The factor loadings of the items on their respective domains were all statistically significant. Rasch analysis indicated disordered categories and the original 10-point scale was subsequently replaced with a 5-point scale. Each VMB domain fitted the Rasch model, showing good metric properties, including unidimensionality (explained variances ≥66% and eigenvalues <1.9), person separation (1.86 to 2.29), reliability (0.87 to 0.94), item fit (infit MnSq’s >0.72 and outfit MnSq’s <1.47), targeting (0.30 to 0.50 logits), and insignificant differential item functioning (all DIFs but one <0.50 logits) from gender, age, and visual status. The three VMB domains correlated significantly with relevant visual, musculoskeletal, and balance assessments, demonstrating adequate convergent validity of the VMB. CONCLUSIONS: The VMB is a simple, inexpensive, and quick yet reliable and valid way to screen and evaluate concurrent visual, musculoskeletal, and balance complaints, with contribution to epidemiological and intervention research and potential clinical implications for the field of health services and low vision rehabilitation.This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially.

The purpose of this work is to identify human neural circuits involved in inhibitionofaccommodation/vergence by contrasting the cortical functions subservient to negative voluntaryaccommodation/vergence (NVA) with those evoked by active fixation in darkness (FIX). Five subjects with normal corrected acuity were studied using positron emission tomography and the H O bolus technique. The dominant right eye viewed a laser speckle pattern (633 nm) whose direction and velocity of motion were determined by the refractive state of the eye. The speckle pattern was presented at a distance of 1.8 m (0.55 D). The non-dominant eye was patched. Subjects performed two tasks counterbalanced for order effects: (i) attempted fixation on the remembered target in darkness with the dominant eye open and ‘fixating’; and (ii) voluntary reduction of the laser speckle flow during each alternate 20-s epoch when a convex +2.0 D lens was placed in front of the right eye causing the speckle pattern to move downwards at 3 °/s. Comparison of the conditionof NVA with the conditionof FIX indicated widespread occipital activation. Decreases in absolute regional cerebral blood flow occurred in the superior parietal cortex (BA 5), frontal cortex (BA 8 and 10) and within the postcentral/precentral gyrus (BA 1/2/3/4) bilaterally where deactivation clusters eclipsed the presumed neck and shoulder areas. Negative accommodation/vergence appears to be driven by a reduction of parasympathetic tone, and has the effect of shutting down brain regions known to be involved in regulating visual search as well as a centrally controlled eye–head–neck–shoulder motor programme responsible for posturing gaze.

A time honored dictum states that the eyes "lead the body", i.e. that the body typically adjust its position to compensate for an impoverished retinal image (e. g., as due to optical blur, and/or inappropriately sized visual target). But only moderate or low level of evidence exists in support of this view. Inconclusive evidence does not, however, equal negative evidence. The accommodation/vergence system does exhibit signs of overload in contemporary working life, including eye discomfort, transient myopia, altered pattern of eye-lens oscillations, and associated phoria. Accommodation/vergence overload, caused by non-ergonomic near work, may also emerge as quickly as within one regular workday. Long-term musculoskeletal consequences of high accommodation/vergence demands have nevertheless not yet been studied in any detail. A research agenda which aims to provide multi-scientific evidence for eye-neck/shoulder interactions with public health implications and which also, in addition, study the eye-neck/shoulder mechanisms and elucidates the operating characteristics, should consequently be highly warranted. This new knowledge would be useful for physiotherapists, ergonomists and opticians, who in their profession treat patients experiencing vision-and musculoskeletal disorders. If both visual and the musculoskeletal aspects are given full and equal weight in the design and evaluation of work places, it is predicted to lead to an improved quality of life for the individual worker, and an enhanced productivity for the employer.

The purpose of this study was to identify the networks involved in the regulation of visual accommodation/vergence by contrasting the cortical functions subservient to eye-lens accommodation with those evoked by foveal fixation. Neural activity was assessed in normal volunteers by changes in rCBF measured with PET. Thirteen right-handed subjects participated in three monocular tasks: (i) resting with eyes closed; (ii) sustained foveal fixation upon a LED at 1.2 m (0.83 D); and (iii) accommodating alternately on a near (24 cm, 4.16 D) vs. a far (3.0 m, 0.33 D) LED alternately illuminated in sequential 2 s epochs. The contrast between the conditions of near/far accommodation and of constant foveal fixation revealed activation in cerebellar hemispheres and vermis; middle and inferior temporal cortex (BA 20, 21, 37); striate cortex and associative visual areas (BA 17/18). Comparison of the condition of constant fixation with the condition of resting with closed eyes indicated activation of cerebellar hemispheres and vermis; visual cortices (BA 17/18); a right hemisphere dominant network encompassing prefrontal (BA 6, 9, 47), superior parietal (BA 7), and superior temporal (BA 40) cortices; and bilateral thalamus. The contrast between the conditions of near/far accommodation with closed-eye rest reflected an incremental summation of the activations found in the previous comparisons (i.e. activations associated with constant fixation). Neural circuits activated selectively during the near/far response to blur cues over those during constant visual fixation, occupy posterior structures that include occipital visual regions, cerebellar hemispheres and vermis, and temporal cortex.

Background: Unlike the usual skeletal muscles, ciliary muscles responsible for focusing the crystalline eye lens and extraocular muscles responsible for convergence eye movements appear resistant to fatigue. Purpose: The dual goals of this article are to briefly outline the current evidence that suggests that probing into blood flow and hemodynamic prefrontal brain activity with Near-Infrared Spectroscopy (fNIRS) could advance progress in visual ergonomic research, and to provide pilot data exemplifying the proposed approach. Methods: The vision task consisted of sustained focusing on a contrast-varying black and white Gabor grating. Four participants with a median age of 46 (IQR 44 – 50) fixated the grating from a distance of 65 cm. Three counterbalanced 10-min tasks required central fixation and accommodation/convergence on the grating target through: (i) 0.0 diopter (D) lenses, (ii) −1.5 D lenses, and (iii) −3.5yD lenses while maintaining maximal focus. Non-invasive measurements of local oxyhemoglobin (HbO2) were quantified with a one-channel Near Infrared Spectrometer, NIRS. The NIRS probe was placed on the prefrontal cortex in the vicinity of the right dorsolateral prefrontal cortex or Brodmann area 46 (DLPFC, BA 46). Accommodation response and contrast threshold was measured in parallel. Results: General estimating equation analyses showed that baseline subtracted DLPFC blood flow (ΔHbO2) increased significantly over time in all three lens conditions. The effect of time may be caused by a continuous increase in mental effort to compensate for progressively more mental fatigue induced by increased visual attention. The increase of DLPFC ΔHbO2 was also larger in magnitude in participants with larger amplitudes accommodation response (i.e., in participants who minimized deterioration in visual performance). Conclusion: The results from this study indicate that oxyhemoglobin changes recorded over DLPFC with NIRS can be used to assay the degree to which the visual system is strained during demanding near work.

This study is concerned with a new method for partly automating forestry harvesting work. Work-related injuries and constant demands for a higher productivity are two of the many arguments for why forestry work must be improved. Forestry work places great mental demands on the driver because they must continuously evaluate and act on relevant parts in a heavy visual information flow. Against this background the purpose of the present study was to extend the knowledge of functional linkages between visual and mental fatigue, performance, and prefrontal cortex activity, during semi-automated and conventional forestry harvesting work. Eleven healthy participants, range 21–51 years old, with a minimum of 1-year work experience, carried out the task of loading logs along a standardized path in a machine simulator during two counterbalanced 45-min periods: (i) conventional forest harvesting, and; (ii) semi-automated forest harvesting. Equal emphasizes was put on accuracy and speed. During manual forest harvesting the driver controlled the crane arm, used to load logs into the load space of the forest vehicle (“forwarder”), by manually operating the joysticks and so guide the crane to the location of the log and then back to the load space. During semi-automatic forest harvesting the driver moved the crane with the press of a button to a pre-programmed location near the log and then, after another button press, to a pre-programmed location within the load space. The following joystick usage parameters were considered for the statistical analysis: Sequential work cycle number, work phase (1-loading in basket, 2-movement to log, 3-picking up log, 4-movement to load space), number of simultaneously used controls across samples of one phase, number of direction changes of joystick movements per phase. Mental load was assessed by quantification of oxygenated hemoglobin (HbO2) concentration changes over the right dorsolateral prefrontal cortex (dlPFC) via non-invasive functional near infrared spectrometry (fFNIRS: PortaLite mini, Artinis Medical Systems, Zetten, the Netherlands). The frequency and duration of horizontal amplitudes of eye/head/neck angles was assessed continuously with 8 SmartEye cameras and used as a measure of visual load. NASA-TLX and Borg CRS was used to assess perceived mental and physical fatigue. Linear Mixed Model will be used to test and to analyze the effect of the duration of work, joystick usage, work type (manual or semi-automated) and perceived mental and physical effort on the outcome of oxygenated hemoglobin concentration. This study contributes with new knowledge of the consequences of the current increase in automation. The 4th industrial revolution can have tremendous implications on how we perceive and organize work in the future, but little is still known about the impact on human body and brain.

27. A Comparison of Mental and Visual Load Resulting from Semi-automated and Conventional Forest Forwarding

The purpose of the present study was to extend the knowledge offunctional linkages between visual and mental load, performance, and prefrontalcortex (PFC) activity, during forestry forwarding work. Eleven healthy participants,range 21–51 years old, with a minimum of 1-year work experience,carried out the task of loading logs along a standardized path in a machinesimulator during two counterbalanced test conditions: (i) conventional cranecontrol, and; (ii) semi-automated crane control. Mental load was assessed byquantification of oxygenated hemoglobin (HbO2) concentration changes overthe right dorsolateral prefrontal cortex (dlPFC) via non-invasive functional nearinfrared spectrometry (fNIRS). Visual, autonomic, and motoric control variableswere measured and analyzed in parallel along with the individual level of performance.Linear Mixed Models (LMM) analysis indicated more mental loadduring conventional crane work. Collectively, our data suggest that fNIRS is aviable tool which can be used in neuroergonomic research to evaluate physiologicalactivity levels in PFC.

This study is concerned with a new method for partly automating forestry harvesting work. Work-related injuries and constant demands for a higher productivity are two of the many arguments for why forestry work must be improved. Forestry work places great mental demands on the driver because they must continuously evaluate and act on relevant parts in a heavy visual information flow. Against this background the purpose of the present study was to extend the knowledge of functional linkages between visual and mental fatigue, performance, and prefrontal cortex activity, during semi-automated and conventional forestry harvesting work. Eleven healthy participants, range 21–51 years old, with a minimum of 1-year work experience, carried out the task of loading logs along a standardized path in a machine simulator during two counterbalanced 45-min periods: (i) conventional forest harvesting, and; (ii) semi-automated forest harvesting. Equal emphasizes was put on accuracy and speed. During manual forest harvesting the driver controlled the crane arm, used to load logs into the load space of the forest vehicle (“forwarder”), by manually operating the joysticks and so guide the crane to the location of the log and then back to the load space. During semi-automatic forest harvesting the driver moved the crane with the press of a button to a pre-programmed location near the log and then, after another button press, to a pre-programmed location within the load space. The following joystick usage parameters were considered for the statistical analysis: Sequential work cycle number, work phase (1-loading in basket, 2-movement to log, 3-picking up log, 4-movement to load space), number of simultaneously used controls across samples of one phase, number of direction changes of joystick movements per phase. Mental load was assessed by quantification of oxygenated hemoglobin (HbO2) concentration changes over the right dorsolateral prefrontal cortex (dlPFC) via non-invasive functional near infrared spectrometry (fFNIRS: PortaLite mini, Artinis Medical Systems, Zetten, the Netherlands). The frequency and duration of horizontal amplitudes of eye/head/neck angles was assessed continuously with 8 SmartEye cameras and used as a measure of visual load. NASA-TLX and Borg CRS was used to assess perceived mental and physical fatigue. Linear Mixed Model will be used to test and to analyze the effect of the duration of work, joystick usage, work type (manual or semi-automated) and perceived mental and physical effort on the outcome of oxygenated hemoglobin concentration. This study contributes with new knowledge of the consequences of the current increase in automation. The 4th industrial revolution can have tremendous implications on how we perceive and organize work in the future, but little is still known about the impact on human body and brain.

Purpose: To extend our knowledge of the functional linkages between visual fatigueand regional cerebral prefrontal cortex (PFC) oxygenation, we measured time related hemodynamic changes over the right dorsolateral prefrontal cortex (dlPFC) duringconvergence load under conflicting stimulus-to-accommodation and stimulus-tovergence eye movements with and without concurrent mental load.

Methods: Twenty healthy participants with a median age of 28 years (range:18–44 years) fixated upon a vertical bar presented separately to the left andright eyes, using polarized filters, during four counterbalanced 10-min periods:(i) no accommodation/vergence conflict (Control, Ctrl); (ii) added convergenceload and accommodation/vergence conflict (Conv); (iii) added cognitive load only(Cog) and; (iv) a combination of added cognitive and convergence load andaccommodation/vergence conflict (Cc). Viewing distance was 65 cm. Non-invasivemeasurements of hemodynamic activity over the dlPFC were quantified by functionalnear-infrared spectroscopy (fNIRS). During the two-convergence load conditions, thehorizontal disparity of the two bars varied dynamically from no disparity to a disparityset 20% below the individual threshold for diplopia. Cognitive load was induced by then-back-2 test which required the subject to memorize and recall the changing colorsof the horizontal bars and decide when a given color was the same as that occurring two colors previously. fNIRS data were averaged over 10-s windows centered at 0, 2,4, 6, 8, and 10 min of each task, subtracted from a 20-s baseline window immediatelypreceding the visual task, and then represented as changes in oxygenated hemoglobin(ΔHbO2); deoxygenated hemoglobin (ΔHHb) and total hemoglobin (ΔtHb).

Results: Linear mixed model analyses showed that hemodynamic activity wassystematically influenced by time (p < 0.001). The group-averaged time-related levelof change across the viewing conditions did not differ when compared with one another(p > 0.05). Larger convergence eye-movement responses under conflicting stimulus-to accommodation,and stimulus-to-vergence over time, increased ΔHbO2 and ΔtHb onlyin condition Cc and after 8 min of task time (p < 0.10 for min-6 and min-8: p < 0.05 for min-10).

Discussion: Collectively, our data suggest that HbO2, HHb, and tHb, recorded over the dlPFC with fNIRS, can be used to assay the degree to which supervisory oculomotorcontrol processes are activated during visually deficient near work.

In an experimental study two levels of oculomotor load were induced via optical trial lenses. Trapezius muscle activity was measured with bipolar surface electromyography and normalized to a submaximal contraction. Sixty-six subjects with a median age of 36 (range 19–47, std 8) viewed a black and white Gabor grating (5 c/deg) for two 7-min periods monocularly through a 0 D lens or binocularly through -3.5 D lenses. The effect of time was separately regressed to EMG in two different subgroups of responders: a High-Oculomotor-Load (HOL) and a Low-Oculomotor-Load (LOL) group. A linear regression model was fitted on group level with exposure time on the x-axis and normalized trapezius muscle EMG (%RVE) on the y-axis. The slope coefficient was significantly positive in the -D blur condition for only the HOL subgroup of responders: 0.926 + Time min 1-7x 0.088 (p = 0.002, r2 =0.865). There was no obvious sign of this activity to level off or to stabilize. These results suggest that professional information technology users that are exposed to a high level of oculomotor load, during extended times, are at an increased risk of exhibiting an increased trap.m. activity.

Mobile technology has revolutionised how we work. It is now relatively easy to work anywhere and anytime, but this has placed the onus on mobile (or flexible) workers to set up their own work environment for comfort and ease of use. Vision is an important driver of posture, and hence visual ergonomics principles are integral for setting up digital devices. If mobile workers do not have visual ergonomics knowledge, or are unable to apply visual ergonomics knowledge to appropriately set up their work environment, then they are at risk of developing visual-related occupational health issues due to exposure to adverse physical work environments.

To address this potential health care issue, we propose the introduction of Visual Ergonomics Health Literacy. This would provide mobile workers (including school children) with the knowledge and skills to set up their work environment for comfort and ease of use, wherever they work. It is important to address this issue now before we have a widespread epidemic of discomfort and injury from not applying sound visual ergonomics principles to work environments.

For 1 week, healthy human participants (n=7) were devoid of normal vision by exposure to prism lenses that optically rotated their perceived world around the line of sight by 180degrees. Adaptation to such prisms involved sustained and vigorous practice of the ability to redirect the unadapted efferent motor command; because prior to all visually guided movements, the to-be executed efferent command was based on incorrect (prismatically reversed) spatial information. The time course of this sort of adaptation was systematically explored in Cooper-Shepard mental rotation (MR) tests and in naturalistic motor-tasks for the purpose of investigating whether mental rotations of the direction of the intended movement share common aspects with the process of MR. A control group (n=7) intermittently exposed to the distorted spatial organization of the central visual field was studied in parallel. The main results were as follows: (a) the MR reaction times (RTs) day 1 with prisms appeared to be very similar to the normal RTs (day 1, noprisms) with the one exception that subjects now responded within a prism (rotated) frame of spatial reference rather than within the environmentally upright. The visuomotor performance became grossly irregular and dysmetric. (b) The majority of the visuomotor adaptation functions began to level off on the 3rd day. (c) The increases in natural motor proficiency were accompanied by a systematic and noticeable decrease in magnitude of the MR Y-intercept obtained from the linear regression line calculated between each subject's RT and the various stimulus angles. MR slopes were stable through days 1-7 for both the experimental and control group. An increased correlation between rotational stimulus angle and RT suggested that the MR function also became progressively more tightly coupled to the stimulus angles. (d) Postadaptation measures of performance indicated the occurrence of selective and minimal adaptation in the natural motor tasks only. It is suggested that these results reflect an improved attentional (strategic) ability to replace incorrect (error producing) control signals with correct (error reducing) control signals. As a result, perceptual-motor start-up processes directly related to spatial coding and to the planning, initiation and correction of the intended direction of motor-or-mental movement improved while the subprocess ("stage") concerned with transformations of such movements remained unchanged. Visuomotor adaptation to inverting prisms engages, and thereby stimulates, a cortical system also invoked in the preparatory process of MR.

The time honoured dictum “the eyes steer the body” has gained additional legitimacy in recent years with the advent of new mechanisms which link the visual and musculoskeletal system with one another. A systematic review of the circumstances, under which a change in accommodation/vergence loads actually lead to alterations in physiological levels of musculoskeletal tonus, or vice versa, therefore, appears timely.

In an experimental study four levels of oculomotor load were induced binocularly. Trapezius muscle activity was measured with bipolar surface electromyography and normalized to a submaximal contraction. Twenty-eight subjects with a mean age of 29 (range 19–42, std 8) viewed a high-contrast fixationt arget for four 5-min periods through: (i) 3.5 dioptre (D) lenses; (ii) 0 D lenses; (iii) individuallya djusted prism D lenses (1–2 D base out); and (iv) +3.5 D lenses. The target was placed close to thei ndividual’s age-appropriate near point of accommodation in conditions (i–iii) and at 3 m in condition( iv). Each subject’s ability to compensate for the added blur was extracted via infrared photorefraction measurements. A bitwise linear regression model was fitted on group level with eye-lens refraction on the x-axis and normalized trapezius muscle EMG (%RVE) on the y -axis. The model had a constant level of trapezius muscle activity – where subjects had not compensated for the incurred defocus by a change in eye-lens accommodation – and a slope, where the subjects had compensated. The slope coefficient was significantly positive in the D (i) and the +D blur conditions (iv). During no blur (ii) and prism blur (iii) there were no signs of relationships. Nor was there any sign of relationship between the convergence response and trapezius muscle EMG in any of the experimental conditions. The results appear directly attributable to an engagement of the eye-lens accommodative system and most likely reflect sensorimotor processing along its reflex arc for the purpose of achieving stabilization of gaze

The purpose of this experimental study was to investigate if sustained periods of oculomotor load impacts on neck/scapular area muscle activity. The static trapezius muscle activity was assessed from bipolar surface electromyography, normalized to a submaximal contraction. Twenty-eight subjects with a mean age of 29 (range 19–42, SD 8) viewed a high-contrast fixation target for two 5-min periods through: (1) -3.5 dioptre (D) lenses; and (2) 0 D lenses. The target was placed 5 D away from the individual’s near point of accommodation. Each subject’s ability to compensate for the added blur was extracted via infrared photorefraction measurements. Subjects whose accommodative response was higher in the -D blur condition (1) showed relatively more static bilateral trapezius muscle activity level. During no blur (2) there were no signs of relationships. The results indicate that sustained eye-lens accommodation at near, during ergonomically unfavourable viewing conditions, could possibly represent a risk factor for trapezius muscle myalgia.

Methods A high-contrast fixation-point stimulus [light-emitting diode (LED)] was introduced into the optical axis of the viewing eye or into the midline in case of binocular viewing. The participants (N=6) were asked to compensate for the blur incurred by adjusting the strength of their eye lens. The participants performed in the following three standardized sequential viewing tasks: (i) resting with eyes open in darkness, (ii) accommodating alternately on a near versus a far LED illuminated sequentially (near–far response), and (iii) sustained fixation upon a LED at near. After the third task, the first and second tasks were repeated once.

Results The main effects of the third task were to decrease the overall rate of binocular accommodative relaxation time (diopters/s) in the repetition of the second task trial. The baseline shifts in individual response times also correlated with changes in the response amplitudes under the binocular stimulus conditions, which required contraction of the ciliary muscle.

Conclusions The results taken as a whole validate a technique of essential interest to applied vision research.

The purpose of this work was to characterise short-(S)-wavelength-sensitive-cone mediated contrast sensitivity (CS) across twenty symptom-free subjects and eight asthenopics, all with normal-unaided-or-corrected visual acuity with no sign of oculomotor dysfunction. Threshold contrast sensitivity was assessed by the von Békésy tracking method from a viewing distance of 2.4 m (0.40 D). Three counterbalanced tasks required central fixation of black-and-white square-wave gratings (1, 5, 10, 14, and 17 cycles deg-1) presented through a low-pass (400 - 450 nm) tinted blue lens: through (i) a 0.0 D lens, (ii) a -1.50 D lens, (iii) a +1.50 D lens while attempting volitional accommodation to minimise blur. Baseline increases in eye-strain, which approached high levels at the end of the experiment, did not differentiate between the two groups of volunteers. Compared with symptom-free subjects, asthenopics exhibited larger magnitudes CS performance in the intermediate spatial frequencies during experimental conditions requiring voluntary increases in accommodation. The residual filtered light may encompass reference wavelengths habitually used by the asthenopics in retinal alignment as an adaptive strategy to spare accommodation from eye-strain. Alternatively, asthenopics, owing to inherent retinal factors, may 'drive' their accommodative system harder than symptom-free subjects.[Supported by the Swedish Council for Working Life and Social Research Grant 2005-0488 to HR.]

The purpose of this work was to characterize contrast sensitivity (CS) under short-wavelength illumination in 20 symptom-free subjects and eight asthenopics: all had normal unaided or corrected visual acuity and no sign of oculomotor disease. Threshold CS was assessed using the von Bekesy tracking method from a viewing distance of 2.4 m (0.40 D). Three counterbalanced tasks required central fixation of black-and-white square-wave gratings (1, 5, 10, 14 and 17 c/deg) presented through a low-pass filter blue lens and (1) a +1.50 D lens; (2) a -1.50 D lens and (3) a 0 D lens, while attempting accommodation to minimize blur. Baseline increases in eye strain, which approached high levels at the end of the experiment, did not differentiate between the two groups of volunteers. All the subjects made evident appropriate accommodation during the low blur condition (0 D); the CS curve exhibited the expected characteristics. When the minus lens was placed before the eyes of the observers the distant square-wave gratings were still seen clearly, the eyes presumably had accommodated by an amount equal to the power of the negative lens. Compared with symptom-free subjects, asthenopics exhibited greater CS at the intermediate spatial frequencies both during the low blur and the minus blur conditions. Asthenopics may exhibit an individualized sensory tendency to react more strongly to shorter wavelengths of light and may therefore reflexively 'drive' their accommodative system harder than symptom-free subjects. This would explain the presence of their asthenopia in the first place. Blue light may, in addition, induce more arousal and higher alertness in this category of participants. This would boost the oculomotor aspects of their performance. These findings add to the current understanding of individual variability in the level of oculomotor loads following strenuous near work.

The effect of neck/shoulder pain on the performance in a hand laterality motor imagery test was studied. Responses to the Cooper and Shepard (1975, Journal of Experimental Psychology: Human Perception and Performance 104 48 ^ 56) hand laterality test were explored in twenty-four individuals with chronic non-specific neck pain and twenty-one subjects with chronic neck pain of traumatic origin (whiplash-associated disorder). Twenty-two controls were also included in the study. Digitalised right- or left-hand stimuli were presented at five different stimulus angles (08, 458 laterally, 908 laterally, 1358 laterally, and 1808). The experimental task was to decide the laterality as fast and accurately as possible. The performance, both reaction time (RT) and accuracy, of the two experimental groups was contrasted with that of the control group. The main results revealed that the subjects afflicted with whiplash injury on the average exhibited a faster response pattern than symptom-free healthy controls. Despite their usculoskeletal deficits and experience of pain these volunteers also exhibited a preserved speed ^ accuracy tradeoff. Longer duration of time with symptoms of neck pain was, moreover, associated with progressively faster RTs. These results point to perceptual learning and may reflect different stages of adaptation to neck pain.